1. Field of the Invention
The present invention relates to a semiconductor manufacturing method which provides epitaxial growth and the like on the surface of a silicon substrate placed in, for example, a reaction chamber, by using reactive gas (corrosive gas).
2. Description of the Related Art
Manufacturing processes for providing a semiconductor circuit such as an LSI on a silicon substrate include selectively and epitaxially growing a silicon thin-film on the surface, providing a pattern comprising an SiO2 film (silicon oxide) on the surface of a silicon substrate W, and epitaxially growing a silicon film in a region where the silicon is exposed, vapor-depositing a single-crystal silicon thin-film (epitaxial layer) having a predetermined concentration of impurity on a substrate for a MOS device comprising a silicon substrate having extremely low resistivity, and the like.
In these manufacturing processes, the silicon substrate is placed inside a process chamber and a reactive source gas is injected therein to grow the epitaxial layer on the substrate.
Other manufacturing processes using reactive gas include a variety of CVD processes for providing a thin-film on a substrate by the reaction of the reactive gas, and etching processes for providing micro-patterns, etc.
The reactive gas used in these semiconductor manufacturing apparatuses comprises a corrosive gas, such as ultra-high purity hydrogen chloride gas or ammonia gas. However, when the gas contains even a small amount of moisture, the metal components used in the apparatus (e.g. in the process chamber, gas supply system, gas discharge system, etc.) become susceptible to corrosion. This leads to hazardous pollution caused by metal (heavy metal) from the metallic sections. Consequently, there is a demand for a highly sensitive method for quantitative analysis of the moisture in corrosive gas inside the process chamber.
Conventionally, the only means of investigating the interrelation between processing conditions and heavy metal pollution, and the interrelation between processing conditions and the characteristics of the reactive gas processing, has been to feed back results obtained by directly analyzing a processed monitor wafer by using chemical analysis (atomic absorption spectrometry, radioactivation analysis, etc.), physical analysis (SIMS, TXRF, etc.), and electrical analysis (DLTS, SPV, lifetime, etc.).
In recent years, means for measuring the moisture content in reactive gas (corrosive gas) comprising a laser moisture measuring device which radiates laser light into the main body of a tube-like cell, connected to a process chamber, and measures the absorption spectrum of the transmitted light, has been proposed in, for example, Japanese Unexamined Patent Application, First Publication (Kokai), No. Hei 5-99845, Japanese Unexamined Patent Application, First Publication (Kokai), No. Hei 11-183366 and the like. Since the laser moisture measuring device can measure the gas without contact with the gas, it can measure even reactive gas with high precision. Therefore, it has become possible to measure the moisture content inside the process chamber even during processing.
However, the conventional semiconductor manufacturing technology described above does not address the following problems. During the actual processing, the moisture content inside the process chamber is not always constant in each process. Even when conditions are set after feeding back the results of analysis of the process monitor wafer, fluctuation in the moisture content causes variation in the characteristics of the reactive gas processing. For example, in the case of the selective epitaxial growth already mentioned, the moisture (absorbed moisture) of the SiO2 film may be removed during pre-processing baking of the substrate, whereby the moisture content inside the process chamber increases. In this case, the moisture content increases during selective epitaxial growth, affecting the characteristics of the selectability of the selective growth and the selectively deposited film.
Furthermore, the moisture within the process chamber does not come only from the reactive gas pipes, and may be caused by atmosphere seeping in from other outside regions. This also increases the moisture content, making it difficult to determine the cause of fluctuations in the moisture content merely by measuring the moisture content in the process chamber. Nor is it clear what level of moisture content within the process chamber will make it possible to adequately control the effects of heavy metal pollution. For example, as shown in FIG. 9, an investigation of the relationship between the recombination lifetime and the moisture of discharged gas during the reaction reveals that the lower the moisture content, the longer the lifetime. However, there is a considerable difference between the average lifetime (solid line) and the maximum lifetime (broken line). This is due to spots of heavy metal pollution on the surface of the substrate.
The present invention has been realized after consideration of the above problems. It is an object of this invention to provide a semiconductor manufacturing method whereby reactive gas processing, such as selective epitaxial growth, can be carried out with high precision by correctly adjusting conditions during processing.
It is another object of this invention to provide a semiconductor manufacturing method and a semiconductor manufacturing apparatus which can restrict increases in the moisture content, prevent heavy metal pollution and the like, and investigate the correlation between moisture content in the process chamber and outside regions.
In order to solve the problems mentioned above, the semiconductor manufacturing method according to a first aspect of this invention provides a semiconductor manufacturing method which performs reactive gas processing, the reactive gas being fed into a reaction chamber, into which a substrate is placed, and reacting with the substrate. The method comprises measuring the moisture content in the reaction chamber, into which the substrate is placed, and in a gas discharge system of the reaction chamber, and adjusting conditions for processing the reactive gas based on the moisture content
In this semiconductor manufacturing method, the moisture content in the reaction chamber, into which the substrate is placed, and in a gas discharge system of the reaction chamber, is measured, and the conditions for processing the reactive gas are adjusted based on the moisture content. Therefore, it is possible to adjust the moisture content itself (correcting it to within an appropriate range) and conditions for film-formation, etching, and the like, based on the measurement of the moisture content during actual processing. This makes it possible to achieve highly precise and stable processing which takes into consideration the effects of moisture content on the characteristics of the reactive gas processing.
Preferably, in the semiconductor manufacturing method according to the first aspect of this invention, the conditions for processing the reactive gas should comprise conditions for heating the substrate prior to feeding the reactive gas into the reaction chamber.
In this semiconductor manufacturing method, the conditions for heating the substrate (baking conditions) are adjusted prior to feeding the reactive gas into the reaction chamber. Therefore, moisture in the substrate can be sufficiently removed prior to feeding the reactive gas into the reaction chamber, and the moisture content inside the reaction chamber can be adjusted to an appropriate level, and the like, thereby making the processing more stable.
The conditions for heating which are adjusted comprise at least one of the heating temperature of the substrate, the heating time of the substrate, and the amount of purge gas.
Preferably, in the semiconductor manufacturing method according to the first aspect of this invention, the conditions for processing the reactive gas should comprise at least one of the heating temperature of the substrate, the amount of the reactive gas, the mixture ratio of the reactive gas, and the pressure inside the reaction chamber.
Adjustment is made to at least one of the heating temperature of the substrate, the amount of the reactive gas, the mixture ratio of the reactive gas, and the pressure inside the reaction chamber. Since these conditions particularly affect the selectability of selective epitaxial growth, the selectability of the selective growth can consequently be increased.
Further, the semiconductor manufacturing method according to the first aspect of this invention comprises reactive gas processing of the substrate, which has silicon oxide provided on at least part of its top face.
In the case of the substrate which has silicon oxide provided on at least part of its top face, there is a danger that the moisture of the silicon oxide will be removed during baking, increasing the moisture content inside the reaction chamber. By measuring the moisture content, even this type of substrate can be processed with high precision and stability.
The semiconductor manufacturing method according to the first aspect of this invention is especially suitable in the case where the substrate comprises a silicon substrate, and the reactive gas processing comprises selectively growing a semiconductor layer in a region on the top face of the substrate where the silicon is exposed.
When selectively and epitaxially growing a semiconductor layer, such as a silicon layer, in a region on the top face of the substrate where the silicon is exposed, the selectability is affected by the moisture. Therefore, selective growth can be achieved with high precision and high selectability by adjusting the conditions based on the measured moisture content.
According to the semiconductor manufacturing method of the first aspect of this invention, the moisture content in the reaction chamber, into which the substrate is placed, and in the gas discharge system of the reaction chamber, is measured, and the conditions for processing the reactive gas are adjusted based on the moisture content. The moisture content itself and conditions for film-formation, etching, and the like, are adjusted based on the measurement of the moisture content during actual processing. Therefore, it is possible to achieve highly precise and stable processing which takes into consideration the effects of moisture content on the characteristics of the reactive gas processing. In particular, in selectively growing a semiconductor layer in a region on the top face of a silicon substrate, the selectability is affected by the moisture. Therefore, stable selective growth can be achieved with high selectability by adjusting the parameters (processing conditions such as heating temperature) which influence selectability, based on the measured moisture content.
The inventors researched the causes of increased moisture content in a reaction chamber, and measured the moisture content in an airtight space of the substrate carrying system, comprising a region outside the reaction chamber, when the substrate is carried into the reaction chamber. As shown in FIG. 10, it was discovered the moisture content in the reaction chamber increases in spite of the fact that the moisture content in the airtight space is decreasing (in FIG. 10, reference code Tr-ch represents data inside a carrying chamber (the airtight space), and Pr-ch represents data inside a processing chamber (reaction chamber)). It is believed that this is because the reaction chamber is heated beforehand to a predetermined temperature, and oxygen entering the airtight space from an outside section, such as a load lock, reacts with hydrogen in the reaction chamber, thereby generating moisture. The carrying system becomes a moisture supply source in addition to the reactive gas.
Based on this knowledge, a second aspect of this invention solves the problems mentioned above and comprises a semiconductor manufacturing method which performs reactive gas processing (corrosive gas processing), wherein, when a substrate carrying system inserts a substrate from an airtight space in the substrate carrying system into a reaction chamber, and when the substrate is ejected from the reaction chamber to the airtight space, reactive gas (corrosive gas) is fed into the reaction chamber and reacts therein. The method comprises a substrate carrying step of measuring the moisture content in the airtight space by means of a first moisture measuring device which is connected to the airtight space, and thereafter, inserting and ejecting the substrate by means of the substrate carrying system; and a gas processing step of performing the reactive gas processing while measuring the moisture content in the reaction chamber by means of a second moisture measuring device, which is connected to the reaction chamber, after the substrate carrying step.
Furthermore, a third aspect of this invention provides a semiconductor manufacturing apparatus for performing reactive gas processing (corrosive gas processing) when a substrate carrying system inserts a substrate from an airtight space in the substrate carrying system into a reaction chamber, and when the substrate is ejected from the reaction chamber to the airtight space. The semiconductor manufacturing apparatus feeds reactive gas (corrosive gas) into the reaction chamber and reacts the reactive gas therein. The semiconductor manufacturing apparatus comprises a first moisture measuring device, which measures the moisture content in the airtight space of the substrate carrying system, and a second moisture measuring device, which measures the moisture content in the reaction chamber.
In the semiconductor manufacturing method of the second aspect and the semiconductor manufacturing apparatus of the third aspect, a first moisture measuring device measures the moisture content in the airtight space of the substrate carrying system, and a second moisture measuring device measures the moisture content in the reaction chamber. Consequently, the moisture content in the airtight space of the substrate carrying system and the moisture content in the reaction chamber can be measured together, making it possible to investigate the effects of moisture content in the airtight space on the moisture content in the reaction chamber. In addition, the moisture content in the airtight space can be measured and reduced in order to reduce moisture content in the reaction chamber, achieving excellent gas processing.
Preferably, in the semiconductor manufacturing method according to the second aspect of this invention, the substrate carrying step comprises inserting the substrate from the airtight space to the reaction chamber or ejecting the substrate from the reaction chamber to the airtight space, after it has been confirmed that the moisture content in the airtight space is lower than a first default value. The gas processing step should preferably commence after it has been confirmed that the moisture content in the reaction chamber is lower than a second default value.
In this semiconductor manufacturing method, the maximum moisture content required in the airtight space when transporting the substrate inside or outside the reaction chamber is preset as a first default value, and the maximum moisture content required when carrying out reactive gas processing without heavy metal pollution and the like in the reaction chamber is preset as a second default value. Therefore, it is possible to achieve stable and excellent reactive gas processing.
In the semiconductor manufacturing method according to the second aspect of this invention, at least the second default value should preferably be lower than 1 ppm.
The inventors investigated the relationship between moisture content in the reaction chamber and heavy metal pollution. It was discovered that when the moisture content is of the order of ppm, spots of heavy metal pollution appeared on the surface of the substrate, but hardly any of these spots were generated when the moisture content was reduced to the order of sub-ppm. Therefore, the semiconductor manufacturing method of this invention is based on this knowledge, and prevents spots of heavy metal pollution by setting at least the second default value to less than 1 ppm.
In the semiconductor manufacturing method according to the second aspect of this invention and the semiconductor manufacturing apparatus according to the third aspect, at least one of the first moisture measuring device and the second moisture measuring device should preferably comprise a laser moisture measuring device which radiates laser light into a tubular cell main body, connected to the airtight space and the reaction chamber, and measures the absorption spectrum of transmitted laser light.
In the above semiconductor manufacturing method and semiconductor manufacturing apparatus, at least one of the first and second moisture measuring devices comprises a laser moisture measuring device. Therefore, the moisture of the gas to be measured can be quantitatively analyzed with high precision and without physical contact.
In a preferred arrangement of the semiconductor manufacturing apparatus according to the third aspect of this invention, a plurality of reaction chambers are provided, and the first moisture measuring device is capable of measuring the moisture content in each of the reaction chambers.
In this semiconductor manufacturing apparatus, the first moisture measuring device can measure the moisture content of a plurality of reaction chambers. Therefore, the reactive gas can be processed at a moisture content which is appropriate for each of the reaction chambers by measuring the moisture content of each reaction chamber.
Preferably, the semiconductor manufacturing apparatus of the third aspect of this invention further comprises a switching unit which can switch an object connected to the first moisture measuring device to any one of the reaction chambers.
This semiconductor manufacturing apparatus comprises a switching unit which can switch an object connected to the first moisture measuring device to any one of the reaction chambers. Therefore, when the switching unit connects the reaction chamber to be measured to the first moisture measuring device, it becomes possible to measure the moisture content in multiple or individual reaction chambers by using the single first moisture measuring device. Consequently, the number of components and the cost can be reduced.
Preferably, in the semiconductor manufacturing apparatus according to the third aspect of this invention, the first moisture measuring device and the second moisture measuring device comprise a single moisture measuring device, and the apparatus further comprises a switching unit which can switch an object connected to the moisture measuring device to the airtight space and the reaction chamber.
In this semiconductor manufacturing apparatus, a single moisture measuring device performs the functions of the first and second moisture measuring devices. The switching unit can switch the object connected thereto to the airtight space or the reaction chamber. Therefore, the moisture content in the airtight space and the reaction chamber can be measured by a single moisture measuring device, reducing the number of components and the cost.
According to the semiconductor manufacturing method of the second aspect of this invention and the semiconductor manufacturing apparatus of the third aspect, the first moisture measuring device measures the moisture content in the airtight space of the substrate carrying system, and the second moisture measuring device measures the moisture content in the reaction chamber. Consequently, the moisture content in the airtight space of the substrate carrying system and the moisture content in the reaction chamber can be measured together, making it possible to investigate the effects of moisture content in the airtight space on the moisture content in the reaction chamber. Therefore, the cause of moisture supplied from the substrate carrying system can be analyzed. Further, the moisture content in the airtight space can be measured and reduced in order to reduce moisture content in the reaction chamber, achieving excellent reactive gas processing. Therefore, reactive gas processing such as crystal growth, thin-film deposition, and etching, can be made excellent and more stable, and it becomes possible to manufacture a high-quality semiconductor manufacturing apparatus, such as a semiconductor substrate and a semiconductor device.